[TwigBundle] Do not clean output buffering below initial level

This resulted in issues with PHPUnit 3.6, which will buffer all output and clean them in the end. Since
we cleaned their buffer, the subsequent clean would raise a warning. This is documented in issue 390 of
the PHPUnit tracker.

Closes #2531.

src/Symfony/Bundle/TwigBundle/Controller/ExceptionController.php

@@ -41,8 +41,9 @@ class ExceptionController extends ContainerAware
         // some Windows configurations where ob_get_level()
         // never reaches 0
         $count = 100;
+        $startObLevel = $this->container->get('kernel')->getStartObLevel();
         $currentContent = '';
-        while (ob_get_level() && --$count) {
+        while (ob_get_level() > $startObLevel && --$count) {
             $currentContent .= ob_get_clean();
         }
 

src/Symfony/Bundle/TwigBundle/Tests/Controller/ExceptionControllerTest.php

@@ -0,0 +1,91 @@
+<?php
+
+/*
+ * This file is part of the Symfony framework.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * This source file is subject to the MIT license that is bundled
+ * with this source code in the file LICENSE.
+ */
+
+namespace Symfony\Bundle\TwigBundle\Tests\Controller;
+
+use Symfony\Bundle\TwigBundle\Tests\TestCase;
+
+use Symfony\Bundle\TwigBundle\Controller\ExceptionController;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Scope;
+use Symfony\Component\DependencyInjection\Definition;
+
+class ExceptionControllerTest extends TestCase
+{
+    protected $controller;
+    protected $container;
+    protected $flatten;
+    protected $templating;
+    protected $kernel;
+
+    protected function setUp()
+    {
+        parent::setUp();
+
+        $this->flatten = $this->getMock('Symfony\Component\HttpKernel\Exception\FlattenException');
+        $this->flatten
+            ->expects($this->once())
+            ->method('getStatusCode')
+            ->will($this->returnValue(404));
+        $this->flatten
+            ->expects($this->once())
+            ->method('getHeaders')
+            ->will($this->returnValue(array()));
+        $this->controller = new ExceptionController();
+        $this->kernel = $this->getMock('Symfony\\Component\\HttpKernel\\KernelInterface');
+        $this->templating = $this->getMockBuilder('Symfony\\Bundle\\TwigBundle\\TwigEngine')
+            ->disableOriginalConstructor()
+            ->getMock();
+        $this->templating
+            ->expects($this->any())
+            ->method('renderResponse')
+            ->will($this->returnValue($this->getMock('Symfony\Component\HttpFoundation\Response')));
+        $this->container = $this->getContainer();
+    }
+
+    protected function tearDown()
+    {
+        parent::tearDown();
+
+        $this->controller = null;
+        $this->container = null;
+        $this->flatten = null;
+        $this->templating = null;
+        $this->kernel = null;
+    }
+
+    public function testOnlyClearOwnOutputBuffers()
+    {
+        $this->container->enterScope('request');
+
+        $this->kernel
+            ->expects($this->once())
+            ->method('getStartObLevel')
+            ->will($this->returnValue(1));
+
+        $this->controller->setContainer($this->container);
+        $this->controller->showAction($this->flatten);
+    }
+
+    private function getContainer()
+    {
+        $container = new ContainerBuilder();
+        $container->addScope(new Scope('request'));
+        $container->register('request', 'Symfony\\Component\\HttpFoundation\\Request')->setScope('request');
+        $container->set('templating', $this->templating);
+        $container->setParameter('kernel.bundles', array());
+        $container->setParameter('kernel.cache_dir', __DIR__);
+        $container->setParameter('kernel.root_dir', __DIR__);
+        $container->set('kernel', $this->kernel);
+
+        return $container;
+    }
+}

src/Symfony/Component/HttpKernel/Kernel.php

@@ -55,6 +55,7 @@ abstract class Kernel implements KernelInterface
     protected $booted;
     protected $name;
     protected $startTime;
+    protected $startObLevel;
     protected $classes;
 
     const VERSION = '2.0.6-DEV';
@@ -120,6 +121,8 @@ abstract class Kernel implements KernelInterface
             return;
         }
 
+        $this->startObLevel = ob_get_level();
+
         // init bundles
         $this->initializeBundles();
 
@@ -421,6 +424,16 @@ abstract class Kernel implements KernelInterface
         return $this->debug ? $this->startTime : -INF;
     }
 
+    /**
+     * Gets the ob_level at the start of the request
+     *
+     * @return integer The request start ob_level
+     */
+    public function getStartObLevel()
+    {
+        return $this->startObLevel;
+    }
+
     /**
      * Gets the cache directory.
      *

src/Symfony/Component/HttpKernel/KernelInterface.php

@@ -179,6 +179,13 @@ interface KernelInterface extends HttpKernelInterface, \Serializable
      */
     function getStartTime();
 
+    /**
+     * Gets the ob_level at the start of the request
+     *
+     * @return integer The request start ob_level
+     */
+    function getStartObLevel();
+
     /**
      * Gets the cache directory.
      *